Mechanisms of Toxicity in C. elegans Models of Transthyretin Amyloidosis

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 DESCRIPTION (provided by applicant): Protein aggregation is a feature of most neurodegenerative diseases, including the transthyretin (TTR) amyloidoses. TTR is a tetrameric protein secreted into the blood by the liver. Compelling evidence suggests that peripheral neurodegeneration in the TTR amyloidoses results from rate- limiting TTR tetramer dissociation, aberrant monomer misfolding and misfolded TTR assembly into a spectrum of TTR aggregate structures. Extracellular aggregation leads to proteotoxicity in tissues not synthesizing TTR by a cell non-autonomous process that we seek to understand via the proposed experiments, and which is not understood for any aggregation-associated neurodegenerative disease. In humans, WT TTR aggregation leads to a cardiomyopathy, whereas aggregation of other TTR mutations leads to a primary neuropathy. Herein, we report the development and partial characterization of transgenic Caenorhabditis elegans models of the TTR amyloidoses, exhibiting TTR aggregation and three cell non-autonomous quantifiable neuronal TTR proteotoxicity-associated cellular and sub-cellular phenotypes with direct relevance to human disease. We will characterize TTR mRNA levels and TTR conformations including tetramers, and misfolded TTR oligomers in these models as a function of aging and correlate these with the neuronal phenotypes observed. Defects in microtubule-based trafficking appear to be a centrally important mechanistic feature of TTR proteotoxicity. The availability of novel small molecule and genetic tools to quantify TTR conformation, as well as the ability to image sub-cellular phenotypes in a single neuron as a function of aging in the same living worm to quantify phenotypic changes affords us an extraordinary opportunity to understand the cell biology and biochemistry of neurodegeneration. Access to the drug tafamidis, which dramatically slows progression of the TTR amyloidoses in humans will also allow us to discern how inhibition of TTR aggregation alters the cell biological and biochemical defects apparently underlying neurodegeneration in these models. To further understand the mechanisms of TTR proteotoxicity at the cellular and molecular level, we will search for modulators of TTR proteotoxicity by identifying suppressors of a locomotion defect exhibited by one of our TTR models in a unbiased forward genetic screen. We have identified candidate suppressors in a pilot screen and showed that some exhibited proper TTR synthesis and secretion, suggesting that this screen could identify tissue specific molecular targets that are relays between the formation of extracellular TTR aggregates and cellular toxicity. These studies will establish TTR C. elegans models as relevant to the study of cell non-autonomous TTR toxicity.